1. Field of the Invention
The present invention relates to a fabrication method of a basic polyvinyl-alcohol-based polymer electrolyte film, particularly to a fabrication method of a basic polymer electrolyte film of blended polyvinyl alcohol and quaternary amine and its application in electrochemical systems.
2. Description of the Related Art
PVA (polyvinyl alcohol) is a stable, non-toxic granular or powdered material and has a color varying from white to pale-yellow. Microscopically, the structural formula of polymeric PVA is (—(CH2—CH—OH)n—). As PVA has hydrophilic hydroxyl radicals, it is highly compatible with water and potassium hydroxide, which also have hydroxyl radicals, and water is just the most effective and economical solvent. When PVA is not polymerized with other materials, it is a chain-like high polymeric molecule, and the length thereof is measured in the unit of the length of a C—C bond, and the length of the chain depends on the degree of polymerization. PVA molecules cohere with covalent bonds and hydrogen bonds and form an amorphous hypo-crystalline material; besides, the high polymeric molecular chain is rotatable, which makes PVA be a flexible polymeric material. When an electrical potential difference is applied to PVA, the coupling interaction of the PVA backbones will create a temporary coordinate bonding on the metallic ions inside the PVA material, and the polymeric PVA molecular chain will be moved; thus, the metallic ions are conducted.
PVA has a hydrophilic hydroxyl group and a non-polar hydrophobic alkyl-based chain; therefore, PVA has a superior water-absorbency (about 30%) and superior water retention ability. In alkaline batteries, a PVA-containing polymer electrolyte film can absorb a great amount of alkaline electrolytic solution, and thus, the solid-state polymer electrolyte film becomes gel-like; even though it is placed inside the battery for a long time, no leakage will appear; therefore, the storage life of the battery can be prolonged. Further, the film made of PVA has the characteristics of superior adhesiveness, solvent-resistance, abrasion-resistance, oxygen-barrier ability and tensile strength.
A Taiwan Patent publication No. 200583781 provides a fabrication method, wherein PVA, alkali hydroxide and water are copolymerized to form a solid-state polymer electrolyte. Refer to FIG. 1 for the detailed steps of this method. Firstly, 10˜20 wt. % of PVA with the average molecular weight of 2,000˜120,000 and 50˜60 wt. % of water is mixed and agitated to dissolve completely in an airtight environment and at the ambient temperature (Step S111); meanwhile, 15˜25 wt. % of alkali hydroxide and 10˜20 wt. % of water is mixed and agitated to dissolve completely in an airtight environment and at the ambient temperature (Step S112); next, the PVA solution and the alkali hydroxide solution are mixed at the ambient temperature, and after both are intermixed completely, the intermixed solution is heated in an airtight environment and at the temperature of 50˜100° C. so that a polymerization reaction can undertake therein, and then, after the polymerization completed, the whole system is cooled down at the ambient temperature (Step S12); lastly, a glass-fiber cloth is placed on a tray, and the cooled glutinous polymeric solution is evenly applied to the glass-fiber cloth at the operational temperature of 40˜80° C. and under the operational humidity of 20-50 RH %, and after 30˜60 minutes, a solid-state polymeric film is thus formed (Step S13). However, in the abovementioned conventional technology, when the amount of PVA is too low, or when the amount of alkali hydroxide is too high, or when PVA and alkali hydroxide are added into water simultaneously, the film is hard to form; when the water content of the film is too low, there is an incomplete polymerization reaction so that the ionic conductivity of the solid-state polymeric film will be reduced. When PVA deteriorates, the backbones thereof will break, and the mechanical strength thereof will decrease. To avoid the abovementioned problem, glass-fiber cloth is used to enhance the structure; although the mechanical strength of the solid-state polymeric film is temporarily increased thereby, the deterioration process of PVA still keeps on, and the mechanical strength of PVA itself is not really increased in the long run.
In addition to the abovementioned conventional technology that the solid-state polyelectrolyte film is purely made of PVA, another Taiwan Patent publication No. 200525806 provides a fabrication method of a basic polyelectrolyte film of blended PVA and polyepichlorohydrin (PECH). Refer to FIG. 2 for the steps of this method. Firstly, 1˜30 wt. % of PVA with the average molecular weight of 10,000˜120,000 and the purity of 80˜99% and 70˜90 wt. % of DMSO (dimethyl sulfoxide) is intermixed for 60˜100 minutes at the temperature of 40-80° C. (Step S211); meanwhile, 1˜30 wt. % of PECH with the average molecular weight of 100,000˜1,000,000 and the purity of more than 50% and 70˜90 wt. % of DMSO (dimethyl sulfoxide) are intermixed for 60˜100 minutes at the temperature of 40-80° C. (Step S212); the PVA solution and the PECH solution are mixed and agitated for about 10˜15 minutes at the speed of 100˜1,500 rpm to blend them completely (Step S22); the completely-blended glutinous polymeric solution is poured on a tray and placed in a thermohydrostat at the temperature of 30-70° C. and under the humidity of 5-30 RH % for 60˜180 minutes so that DMSO can vaporize completely (Step S23); lastly, the DMSO-free polymeric film is soaked in the solution of 20˜50 wt. % of alkali hydroxide with the purity of more than 85%, and after 1˜24 hours, the polymeric film is taken out, and then, the basic polymer electrolyte film of blended PVA and PECH is thus formed (Step S24). In comparison with the solid-state basic polyelectrolyte film purely made of PVA, the solid-state basic polymer electrolyte film fabricated with this method has very tiny pores; therefore, it has superior oxygen-barrier ability, which can retard the reaction between oxygen and electrodes and prolong the life of basic batteries. Besides, similar to PVA, PECH is also highly hydrophilic, and owing to the powerful the hydrogen bonding effect thereof, the blending effect is better; therefore, the mechanical strength of the polymer electrolyte film made of PVA and PECH is higher than that purely made of PVA. However, this conventional technology neither provides a method to really solve the deterioration problem of PVA nor mentions a fabrication method of the polymer electrolyte film of blended PVA and quaternary amine.
In order to effectively solve the deterioration problem of PVA, to enhance the mechanical strength of PVA film, and further to promote the hydrophile and the ionic conductivity of PVA, the present invention proposes a fabrication method of a basic polymer electrolyte film of blended polyvinyl alcohol and quaternary amine, which can be extensively used in various alkaline energy-storage systems.